The present invention is related generally to primary electrochemical cells and is more particularly concerned with a novel cathode material for use in such cells and a method for its formation.
Primary electrochemical cells are utilized for a wide variety of applications and are commonly available in a significant assortment of sizes and shapes. Furthermore, a number of electrochemical systems are known for incorporation into such primary electrochemical cells. A large portion of these systems utilize a carbon cathode material. Typically, the carbon cathode material has been formed as a paste and deposited as such within the electrochemical cell container. Because of the fluid form of this paste, albeit viscous, it was necessary to place a heavy separator between the carbon cathode material and the particular anode material utilized. This separator was required to prevent direct contact between the anode and cathode materials. Necessarily, these separators became quite thick to prevent self-discharge of the cells due to internal shorts between the cathode and anode materials. Such a thick separator material naturally increases the internal resistance of the cell thereby decreasing the output which may be derived therefrom.
In a copending patent application entitled "A Primary Electrochemical Cell and a Preformed Cathode Therefor," by F. Goebel and W. P. Brissette, filed Jan. 9, 1975, and now assigned Ser. No. 539,748 which is assigned to the assignee of the instant application and which is being filed concurrently herewith, a novel preformed porous carbon cathode is disclosed and claimed. This cathode has significant advantages over prior art cathodes; however, when such a cathode is incorporated into larger capacity primary electrochemical cells, such as "D" cells or larger, the cathode structure prevents the cells from fulfilling their complete function. That is, the preformed cathodes have a multitude of miniscule pores over the outer surface through which the electrolytic solution of the cell diffuses. During discharge of the cell, various reaction products are formed. These products can clog the pores in the cathode so that the life of the cell is prematurely terminated.